The direction of tape travel in an automatically reversible tape player has to be reversed when a tape has completed its travel in one direction during its reproduction, recording (both collectively called "play"), fast forwarding and rewinding modes. The reverse action is automatically effected in response to an order from a detecting means which detects the tape end. Such a tape end detecting means is one of the most important elements of a tape player and there are many proposals as to detecting methods. The proposals are divided broadly into two categories: one is electrical detection by means of detection of reel base rotation which is converted into pulses by a switch, photocoupler or the like; and the other is mechanical detection by means of detection of changes of tape tensile force.
The mechanical detection means include a mechanism capable of detecting a tape end by friction between a reel base and a check plate.
More specifically, the mechanism comprises, as shown in FIG. 1, a reel base 1 having a boss 2 integrally formed therewith, a check plate 3 disposed in friction contact with the circumferential surface of the boss 2, and a guide hole 5 formed in the check plate 3 and including a relatively narrower set region 5a and a wider reset region 5b defined by a projection 4 which is the point for tape end detection. The reset region 5b is divided into two parts symmetric with respect to the projection 4 so that the tape end detection may be effected whichever direction the reel base rotates. Thus, the set region 5a and the two parts of the reset region 5b of the guide hole 5 make a configuration like the letter Y as a whole.
A detection plate 6 is pivotally supported by an axle 8, and has an end 6a provided with a check pin 7 for reciprocal movement in the guide hole 5 and another end 6b connected to a mechanism for reversing the tape travel direction and which is actuated when a tape end is detected.
The reciprocal movement of the check pin 7 in the guide hole 5 is effected by a cam 9 linked to the detection plate 6 and rotated by a motor not shown. More specifically, the cam 9 is formed on a rotation plate 10 which is continuously driven by a motor. The cam encircles the rotation axle of the rotation plate 10 and includes a set cam surface and a reset cam surface which gradually extend away from or approach the axle of the rotation plate 10 as shown in FIG. 3. The end 6b of the detection plate 6 is provided with a pin-shaped cam follower 11 contacting the cam surfaces of the cam 9 so that as the cam follower 11 is moved by the cam surfaces toward and away from the axle of the rotation plate 10, the check pin 7 moves in the Y-shaped guide hole 5 from the set region 5a to the reset region 5b, as shown in FIG. 1.
The rotatable plate 10 is also provided with an isolated cam 12 radially outwardly isolated from the cam 9 so that as the cam follower 11 is moved by the isolated cam 12, the check pin 7 moves from one end of the set region 5a remote from the reset region 5b upto the tip of the projection 4 in the guide hole 5, as shown in FIG. 2.
The detection plate 6 is connected to the base plate of the tape player by a spring 13 so that the cam follower 11 is biased toward the cam 9 and the isolated cam 12.
The device performs the tape end detection in the following manner:
(1) FIG. 1 . . . During Tape Travel
As the cam follower 11 moves from the largest radius point A on the set cam surface toward the smaller radius cam surface of the cam 9 along with the rotation of the cam 9, the check pin 7 in the guide hole 5 moves from an intermediate position of the set region 5a toward the projection 4. If the reel base 1 is rotating and the tape is travelling when the check pin 7 gets out of the set region 5a, the check plate 3 shifts due to the friction between itself and the reel base 1. Thus, the check pin 7 contacts one side edge of the wider reset region 5b and moves far into the reset region without engaging the projection 4. So, tape end detection is not carried out. Concurrently, the cam follower 11 passes a detection point B (FIG. 3) of the cam 9 and starts moving along the reset cam surface. When the cam follower 11 reaches the smallest radius point C (FIG. 3) on the reset cam surface, the check pin 7 reaches the deepest position in the reset region 5b of the guide hole 5 and thereafter returns as the cam follower 11 moves toward the larger radius cam surface of the reset cam surface. When the check pin 7 again reaches the tip of the projection 4 and as the cam follower 11 starts moving along the set cam surface beyond a point D which is equally spaced from the rotation axle as to the detection point B, the check pin 7 enters in the set region 5a of the guide hole 5. Due to this, the check plate 3 is returned to its original detectable angle against the friction that exists between it and the reel base 1. As the cam follower 11 further moves toward the largest radius point A, the check pin 7 moves to an intermediate position of the set region 5a, and after the cam follower 11 reaches the largest radius point A, the check pin 7 again moves toward the projection 4.
Thus, while the tape runs, the cam follower 11 movable from the set cam surface to the reset cam surface of the cam 9 merely permits the detection plate 6 to repeat reciprocal movement corresponding to the movement of the check pin 7 between the intermediate position of the set region 5a and the deepest position of the reset region 5b of the guide hole 5. This means that while the detection plate 6 repeats said reciprocal movement, the tape is not exhausted yet. A mechanism (not shown) for reversing the tape travel direction is not actuated during this time.
(2) FIG. 2 . . . Tape End Detection
When the reel base 1 stops the rotation because of the end of a tape, the check plate 3, which was biased in one direction because of the frictional engagement with the reel base, is released from the biasing force. Then, the check pin 7, which reached the projection 4 from the set region 5a of the guide hole 5 concurrently with the arrival of the cam follower 11 at the detection point B from the largest radius point A on the set cam surface, engages the tip of the projection 4 and cannot enter far into the reset region 5b.
The rotatable plate 10 continues to rotate after the check pin 7 engages the projection 4. The detection plate 6 does not pivot clockwise. The cam follower 11 cannot further follow the reset surface of the rotating cam 9 and instead it is located at a position spaced from the rotation axle of the cam 9 a distance equal to the spacing of detection point B from the rotation axle of the cam 9 so as to be outwardly spaced from the smaller radius cam surface. As the rotatable plate 10 further rotates, the cam follower 11 contacts the outer periphery of the isolated cam 12 and is pushed by the isolated cam 12 so that the detection plate 6 rotates in the opposite direction counterclockwise. Since the cam surface of the isolated cam 12 bulges more largely than the largest radius point A of the cam 9, the check pin 7 reciprocates between the tip of the projection 4 and the deepest position of the set region 5a of the guide hole 5. Therefore, the detection plate 6 rotates counterclockwise through a larger angle than it rotates during the tape travel and actuates the tape direction reversing mechanism linked thereto.
It should be noted, however, that the overall cam surface of the cam 9 defines a curved line bulging out in the form of an eccentric circle or an oval as shown in FIG. 3 so that the check pin 7 moved by the cam 9 travels at a substantially constant speed in the guide hole 5. Therefore, the detection point B, which is spaced from the rotation axle the same distance as the entrance of the isolated cam 12, is positioned on the larger radius cam surface with respect to the rotation axle of the cam 9. As the result, the set cam surface for moving the check pin 7 in the set region 5a of the guide hole 5 has a rotation angle smaller than that of the reset cam surface for moving the check pin 7 in the reset region 5b of the guide hole 5.
Since the distance between the largest radius point A and the detection point B is proportional to the rotation angle of the set cam surface, if the rotation angle is small as in the prior art described above, the check pin 7 moves in the first region 5a in a too short time to detect even a momentary repose of the reel base.
To bring a tape pack to a play position in an auto-loading tape player by a motor power, it is necessary to drive the motor when the tape pack is halfway inserted into the tape player. When the tape pack is thereafter fully inserted by the motor, a head and pinch rollers are brought into pressure contact with the tape and start conveying the tape. Therefore, it takes time, that is, the time that is required for displacement of the head and the pinch rollers, between the insertion of the tape cassette and the start of the tape transport.
If the reel base is driven concurrently with the motor energization, the tape will be driven by the reel base throughout the time required for the displacement of the head and the pinch rollers before the play mode is completed, thereby causing a phenomenon called "head-cut" wherein the starting part of the tape is not reproduced. The phenomenon spoils the reproduction particularly when the tape is set in the tape pack so that the beginning of one of music pieces recorded on the tape is positioned just at the play starting position as a result of the music selecting operation.
The most usual measure to prevent the phenomenon is to keep the reel base operatively disconnected from the motor by an idler gear interposed therebetween before the head and the pinch rollers forcibly contact the tape. In this case, the reel base stands still for a short time.
If the prior art tape end detecting device employing the cam as shown in FIG. 3 is applied to the above-described auto-loading tape player, there occurs a problem that the detecting device detects the momentary standstill of the reel base, before the forcible contact of thread, as if the stopping of the reel base was caused by tape exhaustion.
In particular, before the forcible contact of the head, since the check pin 7 remains in the set region 5a of the guide hole 5 as it was upon the preceding tape end detection, and the cam follower 11 contacts the set cam surface of the cam 9, the cam follower 11 reaches the detection point B so early that the detection plate 6 falsely detects a tape end immediately after the rotation plate 10 starts rotating due to energization of the source power because the rotation angle of the first cam portion of the cam 9 is too small.
As the result, whereas the tape is not yet exhausted, the tape travelling direction is reversed so as to change one program to another, or alternatively in another type player, a stop mechanism is actuated to bring back the head and the pinch rollers away from the pressure contact positions and sometimes causes tape pack ejection.